Coupling device



Sept. 23, 1952 w R, Buss 2,611,822

COUPLING DEVICE Filed Feb. 3, 1945 W. RODERIC BLIS-S @3M @Wdfed @wwwPatented Sept. 23, 1952 UNITED vSTATES PATENT OFF-ICE ooUPLING DEVICEwilliam Rosario Bliss, Washington, n. c.

Application AFebruary 3, 1945, Serial No. 576,111 1:?. claims.(01.178444) (Granted under the act of March y3, 1883, as amended AprilA30, 1928; 370 O. G. 757) This invention relates to the problem of-coupling a source of high frequency energy to a low impedance load. Theinvention is more particularly directed to the problem of coupling atuned circuit to a low impedance transmission line.

Whereas the invention has many applications, it lis of special utilityin coupling the tank circuit of a radio transmitter to a low impedancetransmission line feeding the antenna.

vIt is an object of the invention' to provide means matching a lowimpedance transmission line or coupling the line` to ahigh impedanceelectrical network.

^ It is a further object of the invention to provide a highly eicientcoupling network `for feeding a low impedance transmission line.

Yet another object of the invention is `to provide means forelectrically coupling a low impedance transmission line toanothernetwork at high efficiency over` a wide frequency band.

It is a more specific object of the invention to provide means forcoupling a radio frequency generator to a low impedance transmissionline through a coupling device matching the transmission line impedance.

The coupling elements of 'the 'presentzinvention are primarily intendedfor application at vhigh frequency work, where difculty is encounteredin eiiciently transferring large amounts of energy from a tuned circuitto "a low impedance line.

Coupling elements previously used in this field have been relativelyineffective due largely tothe fact that their impedance variesconsiderably with small frequency variations, and further that theirimpedance does not match that of the transmission line.

' The invention will be further described with reference to theexemplary embodiments shown in .the drawing, wherein:

Figure 1 illustrates a circuit diagram, partially schematic, of ahigh-frequency signal transmitting system employing therein anembodiment of the invention.

Figure 2 shows a transmitter circuit similar to Figure 1 in whichanother embodiment of the invention is shown in perspective.

Figure 3 illustrates a, plan view of a portion of the resonant tankcircuit of a transmitter and the modified coupling device shown inFigure 2 in an operating position.

Figure 4 is a perspective view of another embodiment of the invention inwhich a block of dielectric material separates the loopfrom a supportingground plate, and

Figure 5 is a perspective view of another embodiment of the inventionwherein the separated metallic plates form the energy pickup deviceCoupling elements of the present invention may be employed for eitherelectromagnetic Lor electrostatic coupling. The invention as shown inFigure 1 includes an electromagnetic coupling loop. The source of energyin the system ofA Figurel l consists of a resonant circuit'whichylasshown, is a resonant line section II. This sec'- tion comprises lineelements IZ and I3 shorted across one end by conductor I4. Forexcitation the resonant circuit is coupled in an oscillator network, andfor this purpose line I3 is connected to the anode of tube Il).4 `Lineelement I2 is connected through blocking condenser I5 to the .grid oftube I0, which is returned to ground through resistor I'I. Anodepotential is supplied' through radio frequency choke I6. The operatingfrequency may be varied over a range by condenser 9 connected across theopen ends of the line sec` The resonant circuit'llI of Figure 1 iscoupled to a load, shown as antenna 23, through a low impedanceconcentricftransmission line 8. The impedance of line J8 is matched tothat of antenna 23 by transformersection 22. Line 8 thereforeconstitutes a flat line. i 1

Line 8 is coupled to resonant circuit II inductively through loop I8.This loop is specifically constructed to have a characteristic im.-pedance matching that of rline 8. Since this eliminates any electricaldiscontinuity between the coupling element and the line itself, standingwaves with their attendant loss of energyare eliminated from thecoupling element itself. Further, the characteristic impedance of thecoupling element is not dependent upon lthe frequency of excitation, andconsequently maximum coupling may be effected with efficiency over acomparatively Wide band. As a result, in a system such as shown inFigure 1, the operating frequency may be varied by `condenser 9 withoutrequiring attendant adjustment of the coupling y D" is the width of theconducting strip, d is the spacing of the horizontal parallel portionsof the strip, and e is the dielectric constant of the interposingmaterial. In the embodiment shown in Figure 1 air is employed as thedielectric, having a dielectric constant equal of unity. For the normalrange of low impedance lines D is larger than 41.

In the system shown in Figure 1, the transmission line coupling elementI8 is short-circuited at its end, and has a rectangular formation. Iftransmission line 8 is assumed to have a characteristic impedance of 50ohms, the ratio of width to spacing of the coupling element to obtainthis value with air dielectric is substantially 6.5. In the drawings forthe purpose of clarity of illustration, a smaller ratio is shown.Another embodiment of the operating prin- `ciples of the invention isshown in the electromagnetic couplingelement of Figures 2 and 3. As inthe system of Figure 1, the energy is derived from a resonant linesection I I and is coupled into a low impedance concentric line 8, whichis terminated by a matching load not shown. In this formof the inventionthe coupling section comprises a flat conductor positioned above ametallic ground plate. In this construction, the characteristicimpedance of the coupling element as a transmission line also dependsupon the ratio of the Width of the conductor to its spacing from the.ground plate, and also upon the dielectric constant of the interposedmaterial. Due to the fact that one of thetransmission line conductors iseffectively extended to form the ground plate, the characteristicimpedance diifers from that of section I8 shown in Figure 1, and may befound substantially'according to the formula:

D is the width of the upper transmission line member comprising the flatelongated conductor, and d is the spacing between this conductor and theground plate. e is the dielectric constant of the interposed material.

In the embodiment shown in Figure 2 metallic member 24 constitutes theground plate. The transmission line conductor, which is connected to theinner element of concentric line 8, is shown at 2B. This conductor maybe curved in its own plane to form a flat loop above the ground plate,,as is' shown in Figure 2. Ihe upper conductor is positioned aboveground plate 24 on insulating blocks 25.

In order to obtain magnetic coupling to the tuned circuit II shown inFigure 2, the conductor positioned abovethe ground plate is connected atits extremity thereto( electrical contact with ground plate 24.

As in the system shown in Figure 1, it will be vunderstood thatthedimensions and proportions of the coupling element shown in Figure 2 are.f

Asuch as to obtain an impedance match between this element and theconcentric line' 8, in accordance with the formula given above.

A top elevation view of thelsystem'shown in .Figure 2 is disclosed inFigure 3. As is preferable For this purpose end 28 of conductor 2G isturned downwardly to form an for magnetic coupling, the coupling loop 2Sis positioned closely beneath the high current end of the resonant linesection I I.

Whereas in the system of Figures 2 and 3 the average dielectric constantof the material interposed between coupling 26 and ground plate 24 maybe considered to be substantially unity, in

vthe embodimentshown in Figure 4 a dielectric sheet 30 is interposedbetween loop 32 and ground plate 29. It will be understood that thiseffectively lowers the characteristic impedance of the coupling elementin accordance with the dielectric constant of sheet 30. Consequently,the use of a dielectric sheet interposed between the coupling loopandthe ground plate allows further latitude in the design of thecoupling element in order to obtain a match to transmission line 8.

In the system shown in Figure 4, end 34 of the coupling 32 is turneddownwardly through aperture 3l in the insulating member 3D, and is thereelectrically connected to the ground plate. Consequently, this couplingelement may be used for magnetic coupling'in such a system as shown inFigure 2.

An electrostatic coupling element constructed according to theprinciples of the invention is shown in Figure 5. Such elements differfrom those disclosed in Figures 1 through 4 in that the end of thecoupling element is not short-circuited and may be capacitativelyenergized in proximity to a conductor carrying a radio frequencyvoltage, such as the-unshorted end of one of the transmission linemembers of resonant section I I shown in Figure, 1.

Employment of the coupling section for electrostatic energization doesnot affect the dimensions of the device. Consequently, the same may beconstructed according to the above stated formulae, as a transmissionline, or as a hat conductor operating in relation to an extended groundplane. The embodiment shown in Figure 5 constitutes a transmission linesection in al1 respects similarto thatof Figure 1, except that it isopen at the end.V As shown in this iigure the coupling elementslcomprises a pair'of at plates, 35 and 3L Plate 35 is grounded as is thelower member of element I8 of Figure 1 for connection with the externalmember of the concentric line.Y Upper plate 31l is directly connected tothe central-.conductor I9 of the line. As in the preceding embodiments,the g physical dimensions of thecoupling element itself will be selectedin accordance' with the above noted formulae, and 'match the concentriclines impedance without electrical discontinuity.

While there has been described preferred embodiments of this inventionit is obvious to those skilled in the art that various changes andmodications can be made therein without departing from the spirit of theinvention and the scope of the appended claims.

The invention described herein may be manufactured and used by or fortheGovernment of the United States of America for governmental purposeswithout payment of any royalty thereon or therefor. 1 y

1.l In combination, a low impedance radio frequency transmission line,and a coupling element connected -thereto comprising a pair of opposedlaterally extended plate conductors, one of said conductors being formedas a flat loop, the other conductor underlying said loop, saidconductors having a characteristic radio'frequency impedance matchingthat of the line.

2. In combination, a low impedance radio frequency transmission linehaving solid dielectric interposed between conducting members, and acoupling element connected thereto comprising a pair of opposedlaterally extended plate conductors, one of said conductors being formedas a flat loop, the other conductor underlying said loop, saidconductors having a characteristic radio frequency impedance matchingthat of the line.

3. In combination, a low impedance radio frequency concentrictransmission line, and a coupling element connected thereto comprising apair of opposed laterally extended plate conductors, one of saidconductors being formed as a fiat loop, the other conductor underlyingsaid loop, said conductors having a characteristic radio frequencyimpedance matching that of thev line.

4. In combination, a low impedance radio frequency transmission line,and an electromag' netic coupling element connected thereto comprising apair of opposed laterally extended plate conductors forming anelectrically closed circuit, one of said conductors being formedv as aiiat loop and the other of said conductors underlying said loop, saidconductors having a characteristie radio frequency impedance matchingthat of the line.

5. In combination, a low impedance radio frequency transmission line,and an electromagnetic coupling element connected thereto comprising apair of opposed laterally extended plate conductors forming anelectrically closed circuit, one of said conductors being formed as aflat loop, and the other of said conductors underlying said loop andareas within and without said loop, said conductors having acharacteristic radio frequency impedance matching that of the line.

6. In combination, a low impedance radio frequency transmission line,and an electromagnetic coupling element connected thereto comprising apair of opposed laterally extended plate conductors forming anelectrically closed circuit, one of said conductors being formed as afiat loop, and the other of said conductors forming a conducting sheetunderlying the loop area and extending beyond the same, and a soliddielectric interposed between the two conductors, said conductors havinga characteristic radio frequency impedance matching that of thetransmission line.

7. In combination, means for generating a high frequency magnetic iield,a low impedance transmission line, and an electromagnetic couplingelement connected thereto comprising a pair of opposed laterallyextended plate conductors, one of said conductors being formed as a fiatloop, said conductors forming an electrically closed circuit and havinga characteristic radio frequency impedance equal to that of thetransmission line, said coupling element being positioned within saidiield.

-8. In combination, an oscillation generator including a resonant line,a low Aradio frequency impedance coaxial transmission line having innerand outer conductors defining a space of annular cross sectiontherebetween, a solid dielectric filling said space, and a couplingdevice disposed in magnetically coupled relationship with the resonantline and having an impedance equal to the characteristic radio frequencyimpedance of the transmission line, the coupling device comprising twofiat conductive plates arranged in closely spaced parallel planes, oneconductive y plate being connected to the inner conductor of the coaxialline and the other plate being connected to the outer conductor, theconductive plates being connected together at a point removed from theconnection with the transmission line, whereby there is maximum energytransfer to the coaxial transmission line.

9. In combination, a low impedance radio frequency two conductortransmission line having a region between the conductors, a soliddielectric filling said region, capacitative space coupling -meanstherefor consisting of a first laterally extendedfplate conductorconnected to one transmission line conductor, a second laterallyextended plate conductor opposed to the first in spaced relationship'andconnected to the other transmission line conductor, and insulation meansinterposed between the plate conductors of a dielectric constantestablishing their characteristic radio frequency impedance at a valuematching that of the transmission line.

10. .In combination, a low impedance radio frequency two conductortransmission line having a region between the conductors, a soliddielectric iiiling said region, space coupling means therefor consistingof a first laterally extended plate conductor connected to onetransmission line conductor, a second laterally extended plate conductoropposed to the first in at least partially spaced relationship andconnected to the other transmission line conductor, and insulation meansinterposed between the plate conductors of a dielectric constantestablishing their characteristic radio frequency impedance at a. valuematching that of the transmission line.

11. The structure defined in claim 10 further including a resonantcircuit positioned in exciting relation to said coupling means.

12. In combination, a low impedance radio frequency two conductortransmission line having a. region between the conductors, a soliddielectric iilling said region, space coupling means therefor consistingof a iirst laterally extended conductor connected to one transmissionline conductor, a second laterally extended plate conductor larger thanthe first extended conductor and affording a ground plane with respectthereto and in at least partially spaced relation therewith, andinsulation means interposed between the extended conductors of adielectric constant establishing their characteristic radio frequencyimpedance at a value matching that of the transmission line.

W. RODERIC BLISS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS OTHER REFERENCES Reference Data for RadioEngineers, by Federal Telephone and Radio Corporation, pages S22-328,August 1949, Knickerbocker Printing Corp., N. Y.

